In semiconductor processing, a large portion of the yield losses can be attributed to contaminations by particles and films of various nature. The contaminants may be organic or inorganic particles, films formed of polymeric bases, or other ionic based materials. The particles or films may be generated as byproducts in the reaction of reactant gases, by the surrounding environment, by the processing equipment or by the handling of manufacturing personnel. Some contaminants are particles or films generated from condensed organic vapors, solvent residues, photoresist or metal oxide compounds.
Typical problems and the detrimental effects caused by particle or film contaminants are poor adhesion of deposited layers, poor-formation of LOCOS oxides, or poor etching of the underlying material. The electrical properties and the stability of devices built on the semiconductor substrate may also be seriously affected by ionic based contaminants. The various forms of contaminants therefore not only reduce the product yield but also degrades the reliability of the devices built. For instance, contaminant particles can cause a device to fail by improperly defined patterns, by creating unpredictable surface topography, by inducing leakage current through insulating layer, or otherwise reducing the device lifetime. It is generally recognized that a particle contaminant that exceeds one-fifth to one-half of a minimum feature size on a device has the potential of causing a fatal defect, i.e. a defect that causes a device to fail completely. A defect of smaller size may also be fatal if it falls in a critical area, for instance, a particle contaminant in the gate oxide layer of a transistor. In modern high density devices, such as a dynamic random access memory chip, the maximum allowable number of particle contaminants per unit area of the device must be reduced accordingly in order to maintain an acceptable yield and reliability.
For instance, in new process technologies that are developed for 64.about.M Bit DRAM products, the process environment required by the technologies are so stringent that the complete enclosure of the process environment for each process tool is contemplated. The enclosure of the process environment for the process tool results in the creation of a minienvironment concept for the process technologies. Within the enclosure of a minienvironment, an extremely high cleanliness class, i.e., about 0.1 at 0.1 .mu.m, is realized, while the overall production area may have a cleanliness class of 1,000. In order to achieve such cleanliness, the wafer processing and loading/unloading sections of the process equipment must be handled by automated input/output devices. The transport of wafers outside the minienvironment is frequently performed by SMIF pods which keep wafers in a clean condition separated from the outside production environment.
In order to keep the wafers in a state of high cleanliness, the SMIF pods and the wafer cassettes positioned in the pods for holding wafers must be periodically cleaned in a cleaning bath filled with a solvent with ultrasonic energy. In the ultrasonic cleaning bath, a wire basket filled with SMIF pods to be cleaned is first positioned in a support base. The support base with the wire basket is then lowered into a cleaning bath filled with a cleaning solvent such as deionized water (or DI water). The wire basket is made large enough for holding two 8 inch SMIF pod covers or four 6 inch SMIF pod covers frequently resulting in a heavy basket with a weight of approximately 8 kg.
The wire basket is equipped with two horizontal handle bars attached to the two side panels on the basket. To initiate a cleaning operation, an operator must manually lift a wire basket by the two horizontal handle bars and position it into the support base such that the basket may be lowered into the cleaning solvent contained in the cleaning bath. The weight of the wire basket, i.e., the weight of the pod covers plus the weight of the basket itself is sufficient to hold the basket in a stable condition during the ultrasonic cleaning process. The conventional cleaning apparatus described above presents a serious personal injury issue to a machine operator due to the large weight, i.e., approximately 8 kg, of the wire basket that must be lifted and positioned by hand. In order to avoid the personal injury issue, the wire basket is usually loaded not to its full load but instead, only to approximately 70% of the full load or about 5.4 kg. This reduces the personal injury issue at the cost of another processing problem. When the weight of the wire basket is reduced to about 5.4 kg, the wire basket does not have sufficient weight to be held in a stable position during the ultrasonic cleaning process, i.e., the wire basket tends to float in the cleaning solvent. As a result, there is a danger of displacement of the basket from its position in the support base or even the danger of the basket; in flipping over. It is therefore desirable to provide an apparatus that is equipped with locking means capable of locking a wire basket to a support base during an ultrasonic cleaning process such that the lightweight of the basket does not affect the operation of the cleaning process.
It is therefore an object of the present invention to provide an apparatus for cleaning semiconductor tools in a cleaning bath that does not have the drawbacks or shortcomings of the conventional cleaning apparatus.
It is another object of the present invention to provide an apparatus for holding a wire basket in a support base for cleaning in an ultrasonic cleaning process.
It is a further object of the present invention to provide an apparatus for locking a basket in a support base for cleaning semiconductor processing tools loaded in the basket in an ultrasonic cleaning process.
It is another further object of the present invention to provide an apparatus for locking a basket in a support base for cleaning semiconductor processing tools loaded in the basket wherein the basket is locked into the support base by at least two diagonally mounted locking means.
It is still another object of the present invention to provide an apparatus for locking a wire basket to a support base during an ultrasonic cleaning process such that the basket is held in a stable position without the danger of tilting over.
It is yet another object of the present invention to provide an apparatus for locking a wire basket in a support base immersed in a cleaning bath filled with deionized water and energized with ultrasonic energy.
It is still another further object of the present invention to provide a method for locking a wire basket in a support base immersed in a cleaning solution such that ultrasonic energy can be applied to a cleaning solvent contained in the bath for cleaning semiconductor processing tools contained in the basket.
It is yet another further object of the present invention to provide a method for locking a basket in a support base for cleaning in an ultrasonic cleaning bath wherein locking means are provided on the support base which may be slidingly adjusted to accommodate wire baskets of various heights.